In certain high-speed applications such as A/D conversions, in image processing systems such as shown in copending application entitled voltage to current conversion switching system, filed on even date herewith, by Richard H. McMorrow Jr. and Hans Weedon and assigned to the same assignee, incorporated herein by reference, it is desirable to provide integration windows as small as six nanoseconds. In such applications the window should be constant in duration over a short period of time (up to one second) with a precision related to the number of bits of the A/D converter. For example, for a ten bit A/D converter the duration of the window during the one second or less period should be stable and with a precision of one part in a thousand. For a six nanosecond window that is a tolerance of six picoseconds or less. Currently, precision of this degree is accomplished with pulse reflection techniques using unterminated cable delay lines of proper length. This is not easily adjustable: the system has to switch between cables of different lengths to get different delays and thus different pulse lengths. Such precise windows are desirable to generate pulses which time integration periods preliminarily to A/D conversions.